This was it, my first big decision as a dad. What car would I bring my newborn son home in?

Though I live in New York City, a taxi or subway didn't feel quite right. Since I review cars for a living, the world is my automotive oyster.

My son, Max, was born two months premature and after spending several weeks in intensive care, he still seemed fragile. I wanted something tough, something impregnable.

A tank, perhaps. But also something with a dash of style and speed.

So my wife, Miranda, and I arrived at the hospital in a 2013 Mercedes-Benz G550 SUV. This hulk weighs about 2.5 tonnes and is 1.9 metres tall.

The G-Class, or Gelandewagen as it's known in Deutschland, started life in the late 1970s as a military vehicle, serving a number of international armies. In 2007 the Vatican got a customised one for use as the Popemobile. Good enough for that Father, good enough for this one.

The civilian version has been around for more than 30 years and its exterior has changed little. It has body-on-frame construction, like a truck. The front window is upright, the hood, roof and sides flat. Boxy? Well, it's the only vehicle I can think of in this price bracket that could be easily replicated using Lego blocks.

On the big day, car seat secured in the rear, I slapped down on the gas pedal and the G550 bolted, laying a streak of rubber on the street, courtesy of a bison-esque 530Nm of torque. Miranda looked at me pointedly. None of that once we pick up Max.

The G-Class's interior has had a recent upgrade, including a thin navigation screen and nice leather. There's even a Harman Kardon stereo system that nearly washes out the sound from the engine bay, where it sounds like the machinery is masticating a dinosaur.

In a sense, it is. The 2013 model has a very rowdy 5.5-litre V8 with 290kW and it gets an abominable 19.8L/100km in the city, 15.6L/100km highway. But it's not likely that New Zealand or Australia will see the thirsty G550 - though the more powerful, and even more ridiculous, AMG version is coming.

On Park Avenue, we drove around Grand Central Terminal and then through the tricky, narrow corridor of the Park Avenue viaduct. The G550 leaned heavily in the turn; other cars gave us a wide berth. Past 46th Street, taxis parted like the yellow sea as we bucked up the avenue.

At the hospital, we valeted the SUV at the attached underground garage, and retrieved our squawking bundle of joy.

We made it home safely.

Still, the Gelandewagen was originally designed for off-road use, not Park Avenue. It has three separate locking differentials, the kind of 4X4 gear which would allow you to climb a towering cliff.

I didn't want to do a disservice to the machine, Max or myself, so several months later I got hold of the fancier, faster and more expensive version, the G63 AMG. This is the vehicle that New Zealand Benz fans will definitely be seeing some time next year, priced around the same as the current model G55.

If anything, the G63 is louder, brasher and even less sensible: a heavy SUV built to ford rivers, which can also drag-race sports cars. Ideal for drug dealers or "Housewives of Beverly Hills", presumably.

A bigger, healthier Max strapped down in the rear, we headed for the hills. I wanted to get the G63 to a place it rarely goes: the dirt. In the miles it took to get into the backcountry, I tried to ignore both the fuel gauge and the slack steering, which discourages you from getting too aggressive in corners.

Eventually I found an unpaved road that led into state game land. It was a narrow track through thick trees, where I discovered, happily, the first of many deep mud holes. I probably should have crept through the thick, goopy mire.

Instead I gave a hoot and blasted into the pit, spraying mud in all directions. Sadly there were no mountains to climb, where I could have tested the three differentials to their full potential (I did engage them, and they do work).

Back on asphalt, the G63's underside was caked with muck, and the twin exhaust pipes were sending out plumes of steam.

I stole a look into the back to see how Max had enjoyed his first off-road excursion. He was asleep.